Flameholder construction



Oct. 3, 1961 w. E. HELFRICH ET AL 3,002,352

FLAMEHOLDER CONSTRUCTION Filed NOV. 12, 1957 INVENTORS EDMLJND D. BROWNJOHN CHAMBERLAIN WILLIAM E- HELFRICH MMYIQ ATTORNEY F" i (3 I 0\Patented Get. 3, 1981 ice 3,002,352 FLAMIEHOLDER CONSTRUCTION William E.Helfrich, Glastonbury, John Chamberlain,

Manchester, and Edmund D. Brown, South Glastonbury, Conn, assignorsto'United Aircraft Corporation, East Hartford, Conn., a corporation ofDelaware Filed Nov. 12, 1957, Ser. No. 695,566

Claims. (Cl. 6039.72)

This invention relates to fiameholders used for combustion purposes andmore particularly to flameholders of the type useable in powerplantsrequiring combustion in areas having vastly different combustionsupporting characteristics.

It is sometimes required that ignition occur and that combustion besupported in a cold airstream which carries atomized fuel of the typehaving poor low temperature vaporization characteristics. This problemis encountered, for example, inmixing ducted fan engines and in a ductedramjet causing ignition and sustaining combustion with an ordinaryflameholder under these conditions is very difiicult. Experience hasshown that even when large width flameholders are used the flame blowoutlimits encountered confine operation to low velocity, high pressure, anda narrow fuel-air ratio band. Special secondary fuels can be used toproduce a piloted flameholder in the cold airstream area but thispractice brings about the attendant problems and dangers of handling twotypes of fuels in flight, one of which is a precarious pilot fuel.

It is an object of this invention to teach a flameholder constructionwhich uses a single and conventional fuel yet provides a pilotedflameholder.

It is a further object of this invention to teach a flameholderconstruction in which combustion is supported in both a stream of heatedgas and an adjacent stream of cold air carrying a fuel having poor lowtemperature vaporization characteristics.

It is still a further object of this invention to teach a flameholderconstruction in which ignition means are provided to cause ignition andcombustion in a heated gas stream, which combustion causes asubstantially radial flamespreader flow to a flameholder located in acold airstream so as to ignite the cold airstream-fuel mixture and causecombustion thereof to be supported in the relatively stagnant areadownstream of the cold air flameholder.

These and other objects andadv-antages of this invention will becomeapparent from the following detailed description of the drawing inwhich:

FIG. 1 is an external showing of a ducted fan engine partially brokenaway to illustrate an embodiment of our invention.

is injected into combustion chambers 26 by fuel nozzles 28. Followingthis first path, the heated gases then pass through turbine section 20,then through the gas passage 34 which is defined at its outer peripheryby splitter duct 36 and may be defined at its inner periphery bytailcone or inner body 66 and is then introduced to flameholder unit 40for secondary burning within afterburner 22. The original fuel-airmixture originating within conbustion chamber 26 may be chosen to besufficiently rich that unburned fuel is introduced to gas passage 34 andhence flameholder unit 40, or additional fuel may be added by means, forexample, of conventional spray bars 41 within hot gas duct 34. Ignitionof the heated gases which pass through gas passage 34 may be effecteddownstream of flameholder unit 40 by any convenient means such as hotstreak ignition unit 42 of the type taught in United States Patent No.2,780,054 which projects an instantaneous stream of flaming raw fuelthrough combustion chamber 26, turbine 20, and gas passage 34,eventually to ignite the fuel-heated gas mixture which exists downstreamof flameholder unit 40 in the relatively stagnant, low pressurecombustion supporting area formed downstream thereof. After the heatedgas from duct 34 burns within afterburner 22, it is discharged through aconventional exhaust nozzle of the type taught in United States PatentNo. 2,770,944 to atmosphere to perform a thrust generating function.

FIG. 2 is a rear view of our flameholder construction. 0

FIG. 3 is a view taken along line 3-3 of FIG. 2.

Referring to FIG. 1, we see an external showing of a modern aircraftmixing ducted fan engine 10 of the type illustrated in United StatesPatent Nos. 2,458,600, 2,610,- 465, and 2,753,685, comprising an airintake section 12, a first compressor section 14, a second compressorsection 16, a combustion section 18, a turbine section 20, and anafterburner section 22, as well as a ducted section 24. Air entersengine 10 through air inlet 12 and is compressed as it passes throughcompressor stage 14. The air will then follow one of two possibleroutes, the first of which is comparable to passing through a turbojetengine and comprises passing through second compressor section 16 whereit is further compressed and then entering combustion section 18 whereit is heated due to the combustion occurring within combustion cham bers26 which receive fuel through fuel nozzles 28 and fuel manifold 30.Spark plug 32 or other ignition means may be provided to ignite theatomized fuel mixture which The second route available to the compressedair being discharged from compressor section 14 is through ductedpassage 24 which is an annular passage defined by engine outer case 44and splitter duct 36 or parts comparable thereto, all of which arepreferably concentric, coaxial and of circular cross section. Atomizedfuel is introduced to the cold air passing through duct passage 24 byfuel injection pipes 46 which are preferably equally spacedcircumferentially about engine outer case 44. While not essential, itmay be deemed advisable to provide shield 48 which is of circular crosssection and concentric and coaxial with outer case 44, to prevent fuelfrom injection means 46 from contacting the engine outer case 44 andburning thereagainst. The cold air-fuel following this aforementionedsecond route through duct passage is discharged into afterburner unit 22as passing through and around flameholder unit 40. No external orspecial ignition means is provided to ignite the cold air-fuel mixturewhich is discharged from duct passage 24 into afterburner 22 throughflameholder 40, for unit 40 is so fabricated withrelation to theremainder of engine 10 that the combustion occurring at the innerdiameter portion of flameholder unit 40 is directed by aerodynamic flowalong flamespreaders 54 toward the outer diameter area of flameholderunit 40. In view of this aerodynamic flow, the flameholder innerdiameter portion, in pilot flameholder fashion, causes ignition andsustained combustion of the cold air-fuel mixture from duct 24 in arelatively stagnant combustion zone created downstream of the outerdiameter portion of flameholder unit 40. This is the teaching of ourinvention as more fully described in connection with the description ofFIGS. 2 and 3 which follows.

Referring to FIGS. 2. and 3, we see that our flameholder unit 40comprises at least one flameholder 50 or 51 positioned to intercept andreceive the cold air-fuel mixture discharged from duct passage 24 andfurther comprises at least one flameholder 52 or 53 positioned tointercept and receive the heated gas-fuel mixture discharged from gaspassage 34. While two such flamei tween and aerodynamica'lly joinadjacent flarneholders, such as 50 and 51. The number of radialconnecting units 54 required depends on engine size and operatingconditions. Flamespreaders or connecting means 54 are of substantiallyU-shaped or trough-shaped cross section and open in a downstreamdirection with respect to the gas passages and aerodynamicallycommunicate with and join our flameholders, such as 50' and 51, whichare annular rings of U-shaped or trough-shaped cross section, opening ina downstream direction. As will be observed by viewing the connectinglines 56 and 58 between a fiamespreader 54 and adjacent fiameholders, 50and 51, there is an actual intertrough connection between these parts;that is, the trough interior of these parts is joined so that the troughof the flamespreader 54 actually enters into the trough of theflameholders 50 and 51. Flamespreader 54 is shown to be made of twopieces 55 and 57, which join along line 59 or may be curved or straightas shown at 70 and 72 respectively in FIG. 3.

By observing FIG. 3 it will be noted that each flameholder ring isconcentric about axis 60 of engine 10, as is splitter duct 36 and outercase 44, but that each flameholder is spaced axially with respect to theothers so that a fiameholder such as 50, which is to be used to supportthe combustion of the cold air-fuel mixture from duct passage 24, isaxially farther downstream than is a fiameholder such as 52 which isintended to support combustion of the heated gas-fuel mixture dischargedthrough passage 34. Our flarnespreaders 54* are accordingly so inclinedand this arrangement is made to establish an aerodynamic flow from theheated gas fiameholders -2 and 53 toward the cold air flameholders 5Gand 51 so that a heated and ignited or burning fuel-air mixture will becontinuously directed along the trough interior and downstream offlamespreaders 54 into the cold air fiameholders 5t} and 51 from theheated gas flameholders 52 and 53 to serve to ignite and support thecombustion of the cold air-fuel mixture discharged past flameholder unit40 from duct 24.

Flameholder unit 40 is shown to comprise a plurality of thin web-typesupport members 62 which project from the body 64 of flameholder unit 40and attaches to each fiameholder ring, 50 through 54 for support andrigidity purposes. If web support member 62 were to be eliminated, theradial connectors 54 could extend forward of the flameholder rings toform a radial support. Flamehoider body 64' is shown to attach to enginetailcone or inner body -66 by any convenient methods such as welding,but it should be borne in mind that it. could as well be supported bystruts projecting radially inwardly from outer case 4 and such wouldprobably be the case if tailcone 66 terminated upstream of unit 40.

In operation, the heated gas-fuel mixture which. passes through duct 34passes flameholders, 52 and 5 3, creating a relatively stagnant-loWvelocity combustion supporting area downstream thereof, therebypermitting combustion of the heated gas-fuel mixture which is ignitedinitially by our hot streak igniter means 4%. This ignited fuel-airmixture from flameholders 52 and 53 passes substantially radiallyoutward and in the trough of flamespreaders 54 into the trough offlameholders- 50 and 5 1' to cause the ignition of and to permit, inpilot fashion, sustained combustion of the cold air-fuel mixturedischarged from duct 24.

Although only one embodiment of this invention has been illustrated anddescribed herein, it Will be apparent thatvarious changes and.modifications may be made in the construction and arrangement of thevarious parts without departing from the scope of this novel concept.

What is desired by Letters Patent is: v

l. Combustion means comprising an inner body of substantially circularcross section, afirst. duct of sub.-

stantially circular cross. section concentrically enveloping,

said inner body and cooperating therewith to define a :5, first annulargas passage through which hot gases are passed, a second duct ofsubstantially circular cross section and coaxial with and enveloping andforming a second annular gas passage with said first duct through whichcold gases are passed and with said second duct extending rearwardlytherefrom to define a combustion chamber, said first and second annulargas passages having substantially radially aligned outlets each with aninner and an outer diameter, a first annular flameholder ring oftrough-shaped cross section positioned immediately adjacent said firstgas passage outlet and having an inner diameter greater than said innerdiameter of said first gas passage outlet and having an outer diametersmaller than said outer diameter of said first gas passage outlet to beWholly located to intercept said hot gases and establish relativelystagnant combustion supporting areas therein in said combustion chamber,a second annular flarneholder ring of trough-shaped cross section andaxially spaced downstream from said first flameholder and positionedimmediately adjacent said second gas passage outlet and having an innerdiameter greater than. said inner diameter of said second gas passageoutlet and having an outer diameter smaller than said outer diameter ofsaid second gas passage outlet to be wholly located to intercept saidcold gases and establish relatively stagnant combustion supporting areastherein in said combustion chamber, and a radially directed andrearwardly tilted flamespreader of trough-shaped cross section joiningsaid fiameholders and positioned to establish gas flow from said firstto said second flameholder.

2. Combustion means comprising an inner body of substantially circularcross section, a first duct of substantially circular cross sectionconcentrically enveloping said inner body and cooperating therewith todefine a first annular gas passage through which hot gases are passed, asecond duct of substantially circular cross section and coaxial with andenveloping and forming a second annular gas passage with said first ductthrough which cold gases are passed in said combustion chamber, saidfirst and second annular gas passages having substantially radiallyaligned outlets each with an inner and an outer diameter, an annularfiameholder unit attached to and supported by said inner body andincluding at least one annular flameholder ring of troughshaped crosssection and opening in a downstream direction and extendingtransversally of the axis of said ducts and positioned immediatelyadjacent said first gas passage outlet and having an inner diametergreater than said inner diameter of said first gas passage outlet andhaving an outer diameter smaller than said outer diameter of said firstgas passage outlet to be wholly located to intercept said hot gases andestablish relatively stagnant combustion supporting areas therein insaid combustion chamber, and also including at least one annularflameholder ring of trough-shaped cross section and opening in adownstream direction and extending transversally of the axis of saidducts and axially spaced downstream from said fiarneholder in said firstduct hot gas and positioned immediately adjacent said second gas passageoutlet and having an inner diameter greater than said innerdiameter ofsaid second gas passage outlet and having an outer diameter smaller thansaid outer diameter of said second gas passage outlet to be whollylocated to intercept said cold gases and establish relatively stagnantcombustion supporting areas therein in said combustion chamber, andfurther including at least one radially directed and rearwardly tiltedflamespreader of trough-shaped cross section and opening in a downstreamdirection joining said fiameholders and positioned to establish gas flowfrom said first to said second flameholder.

3. In a. ducted fan type engine, an engine outer case, an engine tail.cone concentrically located within said outer case, a; splitter case.concentrically located between said outer case and said tail cone anddefining a substantially axially extending gas passage with each andwith said gas passages having substantially radially aligned outletseach with an inner and an outer diameter and with said engine outer caseextending rearwardly of said outlets to define a combustion chamber,means to pass cold air through one of said passages and hot gas fromsaid engine through the other of said passages, a flameholder unitattached to and supported by said tail cone and including a firstfiameholder ring positioned immediately adjacent said hot gas passageoutlet and having an inner diameter greater than said inner diameter ofsaid hot gas passage outlet and having an outer diameter smaller thansaid outer diameter of said hot gas passage outlet to be wholly locatedto intercept said hot gas and establish a relatively stagnant combustionsupporting area therein in said combustion chamber, a second flameholderring spaced both axially downstream and radially from said firstflameholder and positioned immediately adjacent said cold air passageoutlet and having an inner diameter greater than said inner diameter ofsaid cold gas passage outlet and having an outer diameter smaller thansaid outer diameter of said cold gas passage outlet to be wholly locatedto intercept said cold air and establish a relatively stagnantcombustion supporting area therein in said combustion chamber,

and a fiamespreader joining said flameholders and establishing gas flowtherebetween from said hot gas passage to said cold air passge.

4. In a ducted fan type engine having an axis, an engine outer case ofsubstantially circular cross section, an engine tail cone concentricallylocated within said outer case, a splitter case of substantiallycircular cross section coaxial with and concentrically located betweensaid outer case and said tail cone and defining a first annular gaspassage with said tail cone and further defining a second annular gaspassage with said outer case, said gas passages extending insubstantially an axial direction and having substantially radiallyaligned outlets and With said engine outer case extending rearwardly ofsaid outlets to define a combustion chamber, means to pass heated gasfrom said engine through said first passage, means to pass cold airthrough said second passage, means to add fuel to said heated gas andsaid cold air, a first annular flameholder ring of trough-shaped crosssection and opening in a downstream direction and positioned immediatelyadjacent said first gas passage outlet and having an inner diametergreater than said inner diameter of said first gas passage outlet andhaving an outer diameter smaller than said outer diameter of said firstgas passage outlet to be Wholly located to intercept the first passageheated gas and fuel mixture and establish a relatively stagnant,combustion supporting area downstream thereof in said combustionchamber, means to ignite said heated gas and fuel mixture to causecombustion in said first fiameholder stagnant area, a second annularflameholder ring located axially downstream of said first flameholderand being of trough-shaped cross section and opening in a downstreamdirection and positioned immediately adjacent said second gas passageoutlet and having an inner diameter greater than said inner diameter ofsaid second gas passage outlet and I having an outer diameter smallerthan said outer diameter of said second gas passage outlet to be whollylocated to intercept second passage cold air and fuel mixture andestablish a relatively stagnant combustion supportmg area'downstreamthereof in said combustion chamber, and at least one radially extendingand rearwardly tilted flamespreader of trough-shaped cross section andopening in a downstream direction and establishing a relativelystagnant, combustion supporting area downstream thereof and tilted withrespect to the engine axis and connected to each or" said flameholdersso that the trough interiors of said flameholders and said flamespreaderare joined and establishing gas flow therebetween so that the combustionin said first flameholder stagnant area will pass across saidflamespreader and ignite said cold air and fuel mixture in said secondflameholder stagnant area thereby efiecting combustion in both of saidheated gas and fuel and said cold air and fuel mixtures and establishinggas flow therebetween.

5. In a ducted fan engine, three concentric and coaxial members ofcircular cross section shaped and cooperating to define two concentricannular gas passages having substantially radially aligned outlets andwith the outer of said members extending rearwardly beyond said outletsto define a combustion chamber, means to pass heated gas through one ofsaid passages and cold air through the other, and a unitary flameholderunit attached to and supported solely by one of said members andincluding a first fiameholder ring positioned immediately adjacent saidhot gas passage outlet and having an inner diameter greater than saidinner diameter of said hot gas passage outlet and having an outerdiameter smaller than said outer diameter of said hot gas passage outletto be wholly located to intercept the heated gas, and further includinga second fiameholder ring spaced both axially downstream and radiallyfrom said first flameholder and positioned immediately adjacent saidcold air passage outlet and having an inner diameter greater than saidinner diameter of said cold gas passage outlet and having an outerdiameter smaller than said outer diameter of said cold gas passageoutlet to be wholly located to intercept the cold air of the other ofsaid passages and still further including flamespreader means joiningsaid fiameholder rings.

References Cited in the file of this patent UNITED STATES PATENTS2,482,505 Pierce Sept. 20, 1940 2,672,726 Wolf et a1. Mar. 23, 19542,775,867 Collins Jan. 1, 1957 2,780,916 Collins Feb. 12, 1957 2,798,360Hasen et a1. July 9, 1957 2,835,109 Longwell May 20, 1958 2,872,785Barrett et al. Feb. 10, 1959 2,929,203 Henning 'Mar. 22, 1960 FOREIGNPATENTS 419,779 Italy Apr. 8, 1947 685,944 Great Britain Jan. 14, 1953

